Endometrial effects of long-term low-dose administration of RU486.

ABSTRACT

PIP: At the University of California, San Diego, Medical Center during laparoscopy, reproductive specialists examined samples of endometrial tissue from 9 women being treated for endometriosis with 50 mg/day of RU-486 for 6 months and from 9 untreated women (controls) in the follicular phase of the cycle to determine whether or not low-dose RU-486 affected the endometrium. All 9 women treated with RU-486 had abnormal endometrial morphology. Mild hyperplasia was evident in the functional tissues, especially in the stromal compartment. The cellular stroma were dense and had many mitotic figures. The shape of endometrial glands was not regular in size or shape. RU-486 patients exhibited significantly more estrogen receptor (ER) immunostaining than controls (122.93 vs. 103.2; p 0.002), but progesterone receptor (PR) immunostaining was essentially the same. On the other hand, there were no differences in ER and PR in the endometrial glands. These findings suggest that RU-486 acts as a progesterone antagonist and has a chronic unopposed estrogen effect. They also show that the effect of RU-486 is associated with early to midfollicular phase levels of estrogens.